[basic knowledge] ~ zener diode, triode, amplification circuit, number of logic gate transistors, FPGA device junction temperature range, FPGA loading mode, Schmitt trigger, C language structured prog

1. Zener diode

Zener diode , English name Zener diode, It's also called zener diode . utilize PN Junction reverse breakdown state , The phenomenon that the current can vary in a large range and the voltage is basically unchanged , Made of a diode with voltage stabilizing effect . This diode is a semiconductor device with high resistance up to the critical reverse breakdown voltage . At this critical breakdown point , The reverse resistance drops to a very small value , In this low resistance region, the current increases and the voltage remains constant , Zener diodes are graded according to breakdown voltage , Because of this characteristic , The regulator tube is mainly used as a voltage regulator or voltage reference element . Zener diodes can be connected in series for use at higher voltages , Higher stable voltage can be obtained through series connection .

2. triode

triode , The full name should be semiconductor triode , Also called bipolar transistor 、 Crystal triode , It is a semiconductor device with current control · Its function is to amplify weak signal into electrical signal with larger amplitude value , Also used as contactless switch .

Crystal triode , Is one of the basic components of semiconductor , It has the function of current amplification , It's the core component of electronic circuits .

Triode is made on a semiconductor substrate with two very close apart PN junction , Two PN The junction divides the whole semiconductor into three parts , The middle part is the base area , The two sides are the launching area and the collecting area , The arrangement is PNP and NPN Two kinds of . There are three poles , They are called collectors C, The base B, The emitter E.

3. Amplification circuit

With NPN Type silicon triode as an example ,
We will move from the base B To the emitter E The current of is called the base current Ib;
Put the collector from C To the emitter E The current of is called collector current Ic.
Both of these currents flow out of the emitter , So the emitter E An arrow is used to indicate the direction of the current .

3.1 Amplification of triode

The collector current is controlled by the base current ( If the power supply can supply enough current to the collector ), And the base current changes very little , It will cause a great change in collector current , And the change satisfies a certain proportion ： The change of collector current is the change of base current β times , That is, the current change is amplified β times , So we put β It's called the magnification of a triode (β In general, it is much greater than 1, For example, dozens of , A few hundred ).
If we add a changing small signal between the base and emitter , This will cause the base current Ib The change of ,Ib After the change is magnified , Led to Ic Great changes . If the collector current Ic It's going through a resistance R Of , So according to the voltage calculation formula U=R*I It can be counted as , This resistance The voltage will change greatly . We take the voltage out of this resistor , So we get the amplified voltage signal .

4. Number of logic gate transistors

Not gate 2 individual
NAND gate 4 individual
Or not 4 individual
And gate = And non + Not =6 individual
Or gate = Or not + Not =6 individual

5. FPGA Device junction temperature range

The commercial grade junction temperature range is 0~85 Centigrade ,
The industrial junction temperature range is -40~100 Centigrade .

6. FPGA Loading mode

It can be roughly divided into active and passive .

Active loading is defined as loading by FPGA Control the configuration process , Passive loading means FPGA Only passively receive configuration data .

The most common passive configuration mode is JTAG download bit file .
Active configuration is FPGA Take the initiative to Flash Read and write .

7. Schmidt trigger

Schmidt trigger has two stable states , But different from the general trigger , Schmidt trigger adopts potential trigger mode , Its state is maintained by the input signal potential ; For input signals with two different change directions of negative decreasing and positive increasing , Schmidt flip flops have different threshold voltages .

For standard Schmidt triggers , When the input voltage is higher than the forward threshold voltage , The output is high ; When the input voltage is lower than the negative threshold voltage , The output is low ; When the input is between the positive and negative threshold voltage , The output does not change , In other words, the output turns from high level to low level , Or the threshold voltage corresponding to turning from low level to high level is different . Only when the input voltage changes enough , The output will change , Therefore, this kind of element is named trigger . This double threshold action is called hysteresis , It shows that Schmidt trigger has memory . essentially , Schmidt trigger is a bistable multivibrator .

Schmidt trigger can be used as waveform shaping circuit , The analog signal waveform can be shaped into a square wave waveform that can be processed by the digital circuit , And because Schmidt trigger has hysteresis characteristics , So it can be used for anti-interference , Its applications include immunity in open-loop configurations , And positive feedback in closed loop / Used to implement multivibrator in negative feedback configuration .

8. C Language structured programming

Structured programming method
The top-down ; Gradually refine ; Modular design ; Structured coding ;

9. Interrupt vector address

Interrupt vector address , That is, the address of the storage unit where the interrupt vector is stored , The address of the interrupt service routine entry address .
stay PC/AT In flight , Interrupt vector refers to the entry address of interrupt service program .

10. Parasitic effects

Parasitic effects are those that slip into you PCB And wreak havoc on the circuit 、 It's a headache 、 Small fault with unknown cause . They are parasitic capacitances and inductors that are hidden in high-speed circuits . These include parasitic inductance caused by long package pins and printed wiring ; Pad to ground 、 Parasitic capacitance formed between pad to power plane and pad to printed wire ; Interaction between through holes , And many other possible parasitic effects .

ideally , The wire has no resistance , Capacitance and inductance . But in practice , The wire is made of copper , It has a certain resistivity , If the wire is long enough , The accumulated resistance is also considerable . Two parallel wires , If there is a voltage difference between them , It is equivalent to forming a parallel plate capacitor （ Imagine ）. A magnetic field is formed around an energized wire （ Especially when the current changes ）, A magnetic field produces an induced electric field , Will affect the movement of electrons , It can be said that every actual wire, including the pins of components, will generate induced electromotive force , This is called parasitic inductance .

In case of DC or low frequency , This parasitic effect is not obvious . But under the condition of AC, especially high-frequency AC , The impact is very huge . According to the complex impedance formula , capacitance 、 The inductance will greatly hinder the movement of current under AC conditions , It can be converted into impedance . This parasitic effect is difficult to overcome , It's hard to touch . Only by optimizing the line , Try to use short pins SMT Components to reduce its impact , It is impossible to eliminate it completely .

11. The function of pull-up resistor

The most basic function is ： Clamp the signal line with uncertain state to high level through a resistor ( Pull up ) Or low level ( Next PULL ).

1. Improve circuit stability , Avoid misoperation
   If the key in the pull-up resistance example is not pulled up to the high level through the resistance , Then misoperation may occur at the moment of power on , Because at the moment of power on FPGA The pin level of the chip is uncertain , Pull up resistance R12 The existence of ensures that the pin is in a high-level state , Without misoperation .
2. Improve the load carrying capacity of the output pin
   Affected by other peripheral circuits FPGA Insufficient capacity at output high level , To reach VCC state , This will affect the normal operation of the whole system , The existence of pull-up resistance can enhance the driving ability of the pin .